1. Field of the Invention
The invention relates to a method for depositing a silicon oxide layer.
Silicon oxide layers can be made by the so-called TEOS (tetraethyl orthosilicate) process, through the use of gas phase deposition (CVD--Chemical Vapor deposition). It is known that gas phase deposition is activated by the addition of ozone in a gas flow. A disadvantage of the ozone-activated TEOS process is different deposition characteristics which occur, depending on the base material. The deposition rate is thus lower on a thermal oxide than on silicon.
The publication by K. Fujino, Y. Nishimoto, N. Tokumasu and K. Maeda, entitled: Dependence of Deposition Characteristics on Base Materials in TEOS and Ozone CVD at Atmospheric Pressure, in J. Electrochem. Soc. Vol. 138, No. 2, February 1991, p. 550, proposes an improvement by initially depositing a first layer at a low ozone concentration and subsequently depositing a second layer to the desired layer thickness at a high ozone concentration. That process has the disadvantage of producing two separate layers, so that it is not possible to reliably prevent uneven deposition with the development of bubbles and/or fluctuations in stoichiometry. Moreover, the manipulation involved in the process is inconvenient since the deposition conditions must be setup anew for each of the two layers.
It is known from a publication by the same authors, that was published after the above-mentioned publication, and which is entitled: Surface Modification of Base Materials for TEOS/O.sub.3 Atmospheric Pressure Chemical Vapor Deposition, in J. Electrochem. Soc. Vol. 139, No. 6, June 1992, p. 1690, to use a nitrogen or argon plasma in an ozone-activated silicon oxide gas phase deposition through the use of TEOS. Exposing surfaces to the nitrogen plasma levels off surface energies, so that uniform nucleation of the layer to be deposited can be attained for the ensuing actual TEOS process. When argon plasma is employed, the surface energies are achieved by eliminating the different surface constitution by sputtering off the nonhomogeneous layer. Those processes again produce defective layer quality and inadequate replicability, so that they cannot even be considered for use in production.